Assessment of a theoretical formalism for dose estimation in CT: an anthropomorphic phantom study

Dose assessment in computed tomography (CT) is challenging due to the vast variety of CT scanners and imaging protocols in use. In the present study, the accurateness of a theoretical formalism implemented in the PC program CT-EXPO for dose calculation was evaluated by means of phantom measurements. Phantom measurements were performed with four 1-slice, four 4-slice and two 16-slice spiral CT scanners. Firstly, scanner-specific _nCTDI_w values were measured and compared with the corresponding standard values used for dose calculation. Secondly, effective doses were determined for three CT scans (head, chest and pelvis) performed at each of the ten installations from readings of thermoluminescent dosimeters distributed inside an anthropomorphic Alderson phantom and compared with the corresponding dose values computed with CT-EXPO. Differences between standard and individually measured _nCTDI_w values were less than 16%. Statistical analysis yielded a highly significant correlation (P<0.001) between calculated and measured effective doses. The systematic and random uncertainty of the dose values calculated using standard _nCTDI_w values was about –9 and ±11%, respectively. The phantom measurements and model calculations were carried out for a variety of CT scanners and representative scan protocols validate the reliability of the dosimetric formalism considered—at least for patients with a standard body size and a tube voltage of 120 kV selected for the majority of CT scans performed in our study.     

Non-contrast estimation of diffuse myocardial fibrosis with dual energy CT: A phantom study

BackgroundEstimation of diffuse myocardial fibrosis, substrate for adverse events such as heart failure and arrhythmias in patients with various cardiac disorders, is presently done by histopathology or cardiac magnetic resonance. We sought to develop a non-contrast method to estimate the amount of diffuse myocardial fibrosis leveraging dual energy computed tomography (DECT) in phantoms and a suitable small animal model.Methods and ResultsPhantoms consisted of homogenized bovine myocardium with varying amounts of Type 1 collagen. Fifteen mice underwent sham surgery, no procedure, or transverse aortic constriction (TAC) for 5 or 8 weeks to produce moderate or severe fibrosis, respectively. Phantoms and ex vivo mouse hearts were imaged on a single source, DECT scanner equipped with kVp switching. Monochromatic images were reconstructed at 40–140 keV. Linear discriminant analysis (LDA) was performed on mean myocardial CT numbers derived from single energy (70 keV) images as well as images reconstructed across multiple energies. Classification of myocardial fibrosis severity as low, moderate or severe was more often correct using the multi-energy CT/LDA approach vs. single energy CT/LDA in both phantoms (80.0% vs. 70.0%) and mice (93.3% vs. 33.3%).ConclusionsDECT myocardial imaging with multi-energy analysis better classifies myocardial fibrosis severity compared to a single energy-based approach. Non-contrast DECT can accurately and non-invasively estimate the extent of diffuse myocardial fibrosis in phantom and animal models. These data support further evaluation of this approach for in vivo myocardial fibrosis estimation.     

Effect of scan FOV on CT value and material decomposition measurement in dual energy CT: a phantom study

目的:探讨改变扫描视野是否会对双能CT能谱成像(GSI)时CT值的测定及物质分离的计算产生影响.方法:取清洗干净后消毒灭菌的试管17支,分别注入蒸馏水及不同浓度碘对比剂.17个试管的碘浓度分别为0、0.1、0.2、0.3、0.4、0.5、0.6、0.8、1.0、2.0、3.0、4.0、5.0、6.0、8.0、10.0和20.0 mgI/ml.采用GE Discovery 750 HD CT扫描机,宝石能谱成像(GSI)方式,扫描视野分别选取大(A组)和中等(B组)各扫描一次,共余扫描参数2组相同(转速0.8 s/r,螺距0.984,探测器宽度40 mm).在混合能量、水基和碘基图像上分别测量每组试管的CT值、水及碘含量.ROI选取在试管长轴位的最大截面,大小约392 mm2.采用Pearson相关分析和配对样本t检验进行统计学分析.结果:两组视野的图像,物质分离计算所得碘含量与真实值之间均具有明显相关性(A组r=0.9995,B组r=0.9996,P＜0.001).17个试管A组扫描测量平均CT值为(86.86±131.78) HU,平均水含量为(977.14±10.54)mg/ml,平均碘含量为(3.91±5.37) mg/ml;B组扫描测量平均CT值为(106.89±141.51) HU,平均水含量为(994.39±12.35)mg/ml,平均碘含量为(3.82±5.59) mg/ml.两组CT值及水含量的差异有极显著性意义(P＜0.01),两组碘含量测量值的差异无统计学意义(P=0.19).结论:双能CT能谱扫描能够反映不同浓度碘溶液中的碘含量并能进行定量分析,改变扫描视野可以影响混合能量图像中CT值的测定,但对物质分离计算中碘含量的测定没有显著影响.     

An MRI study of the differences in the rate of thrombolysis between red blood cell-rich and platelet-rich components of venous thrombi ex vivo

Purpose:

To test whether T₁‐weighted MRI can detect the differences in the rate of thrombolysis induced by recombinant tissue plasminogen activator (rt‐PA) between platelet‐rich regions and red blood cell (RBC)‐rich regions of venous thrombi ex vivo.

Materials and Methods:

Each of 21 venous thrombi ex vivo (8 pulmonary emboli and 13 in situ thrombi) was dissected along the longitudinal axis. Half of it was analyzed for the presence of platelet, fibrin, and RBC components by immunohistochemistry and the other half was imaged serially by high‐resolution T₁‐weighted three‐dimensional MRI to assess the progression of thrombolysis. The MR images were analyzed for proportions of the remaining platelet‐rich and RBC‐rich regions.

Results:

Laminated platelet‐rich regions, corresponding to Zahn lines, were confirmed immunohistochemically and by MRI in 18/21 venous thrombi. In T₁‐weighted MR images (TE/TR = 10/105 ms) the mean signal intensity of platelet‐rich regions was on average 2.3 higher than that of RBC‐rich regions. The rate of thrombolysis in platelet‐rich regions was on average 30% lower than in RBC‐rich regions. After 120 min of thrombolysis the proportion of lysed platelet‐rich regions was 0.27 ± 0.04 versus 0.40 ± 0.08 in RBC regions, which resulted in 1.4% decrease of lysed thrombus volume per 1% increase of platelet‐rich content.

Conclusion:

Venous thrombi are most often composed of interspersed platelet‐rich and RBC‐rich regions. T₁‐weighted MRI is capable of noninvasive discrimination between those two components of venous thrombi ex vivo which have a different susceptibility to thrombolysis by rt‐PA. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Differentiation of neoplastic from bland macroscopic portal vein thrombi using dual-energy spectral CT imaging: a pilot study

Objectives

To assess the feasibility and value of dual-energy spectral computed tomography (DESCT) imaging for differentiating neoplastic from bland macroscopic portal vein (PV) thrombi.

Methods

Computed tomography (CT) images of 44 patients with macroscopic PV thrombus (bland group, n?=?16; neoplastic group, n?=?28) were reviewed. Iodine-based material decomposition images in the portal venous phase were reconstructed to compare the iodine indices between groups, including thrombus iodine density (I _T), thrombus–aorta iodine density ratio (I _T/I _A), and thrombus–PV iodine density ratio (I _T/I _P). Differential diagnostic performances of DESCT were calculated in the subgroup of 21 patients with histopathological evidence (bland group, n?=?12; neoplastic group, n?=?9).

Results

The iodine indices of the neoplastic group were significantly higher than those in the bland group (P?I _T of 1.14?mg/mL, I _T/I _A of 0.17, and I _T/I _P of 0.17 in the portal venous phase yielded 100?%, 88.9?%, and 100?% sensitivity, and 91.7?%, 91.7?%, and 83.3?% specificity, respectively, in differentiating neoplastic from bland PV thrombi.

Conclusions

DESCT imaging with quantification of thrombus iodine density in the portal venous phase appears to be a promising new method for distinguishing neoplastic from bland macroscopic PV thrombi.

Key Points

? Differentiating the nature of portal vein thrombus is of great clinical significance. ? Iodine-based material decomposition imaging reflects iodine distribution after contrast media administration. ? Dual-energy CT with iodine quantification can distinguish bland from neoplastic PV thrombi.     

应用双能谱CT成像区分肿瘤性与非肿瘤性肉眼可见的门静脉血栓的初步研究

目的评估双能谱CT(DESCT)成像鉴别肿瘤性与非肿瘤性肉眼可见门静脉血栓(PV)的可行性及其价值。方法本研究对44例肉眼可见PV血栓病人(非肿瘤组16例,肿瘤组28例)行CT扫描。门静脉期碘制剂分解的图像用以比较组间碘指数,包括血栓碘浓度(IT)、血栓/主动脉碘浓度比(IT/IA)和血栓/PV碘浓度比(IT/IP)。亚组中21例病理组织学证实(非肿瘤组12例,肿瘤性组9例)的病人估算DESCT的鉴别诊断性能。结果肿瘤组中的碘指标均明显高于非肿瘤组(P<0.001)。门静脉期区别肿瘤性与非肿瘤性PV血栓的门静脉期阈值分别为IT1.14mg/mL、IT/IA0.17、IT/IP0.17,敏感度分别为100%、88.9%和100%,特异度分别为91.7%、91.7%和83.3%。结论门静脉期血栓碘浓度量化DESCT成像在区分肿瘤性与非肿瘤性肉眼可见门静脉血栓方面是一种很有前景的新方法。     

Acute pancreatitis: value of CT in establishing prognosis

The presence and degree of pancreatic necrosis (30%, 50%, or greater than 50%) was evaluated by means of bolus injection of contrast material and dynamic sequential computed tomography (CT) in 88 patients with acute pancreatitis at initial and follow-up examinations. Pancreatic necrosis was defined as lack of enhancement of all or a portion of the gland. Length of hospitalization, morbidity, and mortality in patients with early or late necrosis (22 patients) were evaluated and compared with the same criteria in the rest of the group. Patients with necrosis had a 23% mortality and an 82% complication rate; patients without necrosis had 0% mortality and 6% morbidity. When only the initial assessment was considered, patients with peripancreatic phlegmons and necrosis had 80% morbidity, compared with 36% morbidity in those with phlegmons and no necrosis. Serious complications occurred in patients who initially had or developed more than 30% necrosis. A CT severity index, based on a combination of peripancreatic inflammation, phlegmon, and degree of pancreatic necrosis as seen at initial CT study, was developed. Patients with a high CT severity index had 92% morbidity and 17% mortality; patients with a low CT severity index had 2% morbidity, and none died.     

CT evaluation of solitary pulmonary nodules: value of 185-H reference phantom

The pulmonary nodule CT reference phantom is widely used in the evaluation of nodules 2 cm or less in diameter. It is used to detect benign patterns of calcification that are not visible on thin-section CT scans. Since 1986, the reference nodules have been manufactured with a nominal composition of 185 H. The multicenter study published in 1986 used nodules with a nominal composition of 264 H, 100 H more than the threshold value reported by Siegelman et al. in 1980. In the multicenter study, one of 37 nodules diagnosed as benign with the phantom proved to be malignant. The purpose of this study was to determine the misdiagnosis rate with the 185-H phantom and to ascertain whether the malignant tumors predicted to be benign actually contained calcification. We retrospectively reviewed 296 cases in which examinations had been performed with the 185-H nodules since 1986. Eighty-five nodules were diagnosed as benign by comparison to the reference phantom. These 85 contained no visible calcification on thin-section CT scans. Ten of the 85 cases were shown to be malignant tumors. Eight were diagnosed as having a high probability of benignity. Two were diagnosed as having a moderate probability of benignity. Calcium was present in the tissue of all six nodules available for review. Fifty-nine of the 85 nodules were still clinically indeterminate at the time of this review. Even if all of the clinically indeterminate nodules are benign, the misdiagnosis rate would be significantly higher than in most previous studies. Although analysis by using the reference phantom with 185-H nodules may indicate a high probability of benignity, close radiologic follow-up is necessary.     

Influence of difference in cross-sectional dose profile in a CTDI phantom on X-ray CT dose estimation: a Monte Carlo study

The longitudinal dose profile in a computed tomography dose index (CTDI) phantom had been studied by many researchers. The cross-sectional dose profile in the CTDI phantom, however, has not been studied. It is also important to understand the cross-sectional dose profile in the CTDI phantom for dose estimation in X-ray CT. In this study, the cross-sectional dose profile in the CTDI phantom was calculated by use of a Monte Carlo (MC) simulation method. A helical or a 320-detector-row cone-beam X-ray CT scanner was simulated. The cross-sectional dose profile in the CTDI phantom from surface to surface through the center point was calculated by MC simulation. The shape of the calculation region was a cylinder of 1-mm-diameter. The length of the cylinder was 23, 100, or 300 mm to represent various CT ionization chamber lengths. Detailed analyses of the energy depositions demonstrated that the cross-sectional dose profile was different in measurement methods and phantom sizes. In this study, we also focused on the validation of the weighting factor used in weighted CTDI (CTDI _w ). As it stands now, the weighting factor used in CTDI _w is (1/3, 2/3) for the (central, peripheral) axes. Our results showed that an equal weighting factor, which is (1/2, 1/2) for the (central, peripheral) axes, is more suitable to estimate the average cross-sectional dose when X-ray CT dose estimation is performed.     

管电压对CT值测量、辐射剂量及图像质量影响的模型研究

目的 探讨降低管电流和管电压对CT值的影响,及其辐射剂量降低对图像质量的影响程度.方法 配置不同浓度对比剂样本共113个,在15种不同扫描条件下进行CT扫描.测量和记录CT值及标准差,分析改变管电流和管电压对CT值测量的影响,并计算对应关系.记录CT容积剂量指数(CTDIvol),计算15种扫描条件下的辐射剂量.不同管电压和管电流下CT值差异比较采用方差分析和Kruskal-Wallis秩和检验,不同管电压下CT值对应关系及管电压和管电流对辐射剂量和图像质量的影响程度分析采用相关性分析.结果 管电压固定时不同管电流间(250、200、150、100和50 mA)的CT值差异均无统计学意义(F值分别为0.001、0.008、0.075,P均＞0.05).管电流固定时,不同管电压间(120、100和80 kV)的CT值差异均具有统计学意义(H值分别为17.906、17.906、13.527、20.124、23.563,P均＜0.05).计算不同管电压下同一样本CT值的对应关系:CT值100 kV=1.561×CT值120kV+4.0818,CT值80kV=1.2131 ×CT值120 kV+0.9283.分析不同管电压下辐射剂量对图像噪声的影响程度,并确立相关性方程:N120kv=-5.9771Ln(D120kV)+25.412,N100kv=-10.544Ln(D100 kV)+36.262,N80 kv=-25.326Ln(D80 kv)+62.816.计算噪声值关键点,证明根据所需图像噪声值(11.2和13.9),可以指导扫描条件,在一定条件下应用低管电压,高管电流可以降低辐射剂量.结论 管电压对CT值测量有影响,根据所需图像噪声值调整扫描条件,在一定条件下应用低管电压,高管电流可以降低辐射剂量.改变管电压后造成的CT值变化,可依据不同管电压下CT值对应关系进行校准.     

Intraarticular fractures of the calcaneus: value of CT findings in determining prognosis.

The prognosis of intraarticular calcaneal fractures is variable, ranging from severe functional impairment and pain to complete return of normal function. Clinical assessment and CT scanning were performed 1-11 years after fracture in 45 patients (51 fractures) to determine the relationship between the CT findings and clinical status. Conservatively treated (n = 18) and surgically treated (n = 33) fractures were assessed. Clinical assessment included evaluation of subjective parameters (pain, activity, gait, and use of orthotics) and objective measurement of subtalar motion. CT evaluation included assessment of abnormalities in the posterior subtalar joint, loss of calcaneal height, tendon abnormalities, and calcaneocuboid joint abnormalities. A poor clinical outcome, caused by loss of subtalar motion, was more common when CT showed incongruity or degeneration of the posterior facet (p = .04) and when Bohler's angle was decreased (p = .0006). Other CT findings, such as loss of calcaneal height and tendon abnormalities, did not correlate with clinical outcome. An unexpected finding was that surgical screws were intraarticular in eight (24%) of 33 surgically treated patients; however, this finding was not significantly associated with poor clinical outcome. Our findings indicate that the CT findings of degenerative change and incongruity of the posterior subtalar joint correlate significantly with poor clinical outcome.     

Imaging of small high-density structures in CT A phantom study

RATIONALE AND OBJECTIVES: The aim of this work is to study how the limited spatial resolution of a computed tomographic (CT) system affects the imaging of small high-density structures. This knowledge is relevant not only to understand and interpret clinical data, but also to apply and develop quantification methods for calcifications and stented vessels. MATERIALS AND METHODS: A dedicated phantom containing small differently sized aluminum cylinders was imaged on a 64-slice multidetector row CT (MDCT) while varying acquisition and reconstruction parameters from a high-resolution protocol. In addition, a bead phantom was imaged to estimate the point spread function (PSF) for the different parameter settings. The accuracy in determining object density and size was established for various imaging protocols and compared with simulations based on the estimated PSF. RESULTS: Attenuation values and size measurements were accurate for objects larger than two times the size of the system PSF at the full-width-at-half-maximum. For smaller objects, attenuation values were increasingly underestimated and size was increasingly overestimated. The convolution kernel had the most influence on object signal and size. Use of edge-enhancing kernels yielded more accurate size measurements and higher signal for small objects. However, their application was constrained by noise amplification and edge-ringing artifacts, which led to lower signal-to-noise ratio, degrading the visualization of low densities and small high-density objects. CONCLUSION: Results presented in this report provide insight into limitations in the quantification of small high-density structures and their effect on the visualization of surrounding tissues with recently developed MDCT systems.     

CT仿真内窥镜技术的模型研究

目的　系统分析主要扫描参数对CT仿真内窥镜 (CTVE)图像质量的影响 ,寻找可获得较好图像质量的扫描参数组合。评价CTVE对不同大小、形态的模拟病变的分辨能力 ,进一步确定图像的真实性。方法　应用不同扫描参数分别对不同组别模拟病变的模型进行扫描 ,观察图像质量及模拟病变的分辨情况。结果　准直器宽度、螺距、重叠重建率及重建方式的变化均会不同程度地影响CTVE图像质量。在准直器宽度≤ 3mm、螺距 1.0～ 2 .0、重叠重建率 6 0 %、标准 (STD)重建方式的参数范围内可获得较满意的图像质量 ,并具有可分辨微小结构及较真实显示结构形态的能力。结论　适当选择扫描参数、有效分辨伪影及变形 ,CTVE技术将成为显示空腔脏器病变及结构的有效方法之一。     

螺旋CT肺动脉造影诊断肺小动脉血栓的实验研究

目的：评价螺旋CT肺动脉造影（spiral CT pulmonary angiography，CTPA）诊断犬肺小动脉血栓栓子（直径2.5-3.5mm）的应用价值。方法：23条实验犬行CTPA空白对照后，制成犬自体血块肺动脉栓塞模型，先后行CTPA与X线肺动脉造影（X-ray pulmonary angiography，XPA）检查，由2名医生在工作站上分析所获图像，并与犬肺病理解剖结果对照，评价CTPA与XPA对肺动脉血栓栓塞的诊断价值。结果：22条犬完成实验全过程，病理解剖发现肺动脉内栓子110个，与人工注入栓子数目相符，均位于肺动脉的段或亚段水平，其中107个位于扫描野内。CTPA发现栓子90个，诊断肺动脉内小血栓栓子的敏感度为84.1％，阳性预测值为93.8％；XPA发现栓子82个，敏感度为76.6％，阳性预测值为94.3％。结论：CTPA对实验性肺小动脉血栓栓子有较高的诊断价值。     

Pulmonary nodule size evaluation with chest tomosynthesis and CT: a phantom study

Objective:

We compared digital tomosynthesis (TOMO) and chest CT in terms of assessing the sizes of nodules located in zones where evaluation by simple radiography is limited.

Methods:

A total of 48 images comprising phantom nodules of four sizes in six different locations were used. Nodule size measurement errors for measurements using TOMO and CT images compared with the actual size from each observer were calculated. The inter- and intraobserver repeatability of the measured values and the agreement between the two techniques were assessed using the method described by Bland and Altman.

Results:

The mean measurement errors for all of the nodules and four observers were −0.84 mm [standard deviation (SD), 0.60 mm] on TOMO and −0.18 mm (SD, 0.71 mm) on CT images. The mean measurement errors for the different observers ranged from −1.11 to −0.55 mm for TOMO and from −0.39 to 0.08 mm for CT. Assessing the agreement between nodule size measurements using TOMO and CT resulted in mean measurement errors of −0.65 mm, with a 95% limit of agreement of −2.53 to 1.22 mm for comparison of TOMO with CT.

Conclusion:

Our results suggest that nodule sizes obtained using TOMO and chest CT are comparable, even for nodules located in areas where the size measurement is limited on simple radiography.

Advances in knowledge:

TOMO and CT can be used interchangeably, even for nodules located in a blind area on simple radiography.Solitary lung nodule detection has increased owing to the widespread use of CT imaging. Nevertheless, the most commonly used routine examination for lung nodules continues to be chest radiography, because it uses low radiation doses, is economical and is easy to use. Because chest radiographic images are two-dimensional projections of three-dimensional structures, early lung cancer detection on chest radiographs is often challenging. The projection of pulmonary vessels, bones and part of the mediastinum on lung fields often partially or completely obscures the pulmonary nodules, resulting in failure by the radiologist to detect lung nodules.^1,2Digital tomosynthesis (TOMO) has recently been applied to chest imaging for the detection of subtle nodules on simple radiography, with promising results.^3,4 It has been introduced as a modality with the potential to provide images similar to CT but at a comparably reduced cost and radiation exposure.⁴ James et al⁵ reported that 74% of lung nodules ≥4 mm in diameter that can be identified on CT can also be detected using TOMO. Vikgren et al⁶ also reported that 92% of nodules ≥4 mm in diameter are detectable using TOMO. In 2012, Johnsson et al⁷ compared the ability of TOMO and CT to detect nodule size in 20 patients and found that both methods could be used interchangeably for these measurements. This result calls for caution, however, because the limit of agreement (LOA) between the modalities is wider than for the intraobserver variability of each modality.Based on these studies, we hypothesized that TOMO is comparable to CT imaging for the detection of nodules located in areas where size measurement is limited using simple chest radiography because of overlapping structures. The purpose of this study was to assess the size determination of nodules located in these zones by TOMO and chest CT.     

Imaging factors influencing spine and cord measurements by CT: a phantom study

Metrizamide computed tomography (CT) of the spine allows evaluation of the contents and measurement of the size of intracanalicular structures. The relative size (linear and area measurements) of spinal structures can be changed by varying imaging factors or the density of intrathecal contrast material. Two phantoms, one consisting of rods embedded in a plastic cylinder and the other of a vertebral body with a central rod simulating spinal cord, were evaluated with varying imaging factors (window width and window level) and different contrast concentrations within the surround. It was found that wide window widths allowed the most consistent measurements independent of window level, that a window level midway between the CT number of rod and surround would facilitate uniform measurements independent of window width, and that the use of high concentrations of contrast material (high CT number) in the surround, in combination with a wide window width, was most effective in establishing consistent measurements.     

CT angiography of various superficial femoral artery stents: an in vitro phantom study

Purpose

To evaluate CT reconstruction parameters to improve stent lumen visualization in vitro.

Material and methods

12 latest superficial femoral artery (SFA) stents were placed in a vessel phantom (diameter 4.7 mm, intravascular attenuation 250 HU, extravascular density 50 HU). Stents were imaged with a 128-slice scanner (SOMATOM Definition Flash, Siemens, Germany) with standard parameters: 120 kV, 200 mAs, collimation 128 mm × 0.6 mm. Different reconstruction parameters were evaluated: B26f, B30f, B45f, B46f and B60f kernel; slice thickness of 0.6, 2.0 and 5.0 mm. To measure visualization characteristics, stent lumen diameter and intraluminal attenuation were assessed.

Results

Best stent lumen visualization could be obtained using the B46f kernel (p < 0.001). The visible stent lumen ranged from 66.4% to 83.3% with a mean diameter of 77.7 ± 4.6%. Nitinol stents showed a significant improved lumen visibility compared to the cobalt–chromium stent (p = 0.02). The most realistic lumen attenuation was achieved using the B46f kernel with a mean attenuation of 259.3 ± 8.9 HU. The visible lumen diameter in protocols with 5 mm slice thickness was significantly lower (70.0 ± 4.9%) compared to thinner slices (p < 0.001).

Conclusion

CTA of SFA stents should be reconstructed with a slice thickness of 2.0 mm and a B46f kernel to achieve best image quality and to become more sensitive to exclude instent restenosis.     

Radiation dose and cancer risk from pediatric CT examinations on 64-slice CT: A phantom study

Objective

To measure the radiation dose from CT scans in an anthropomorphic phantom using a 64-slice MDCT, and to estimate the associated cancer risk.

Materials and methods

Organ doses were measured with a 5-year-old phantom and thermoluminescent dosimeters. Four protocols; head CT, thorax CT, abdomen CT and pelvis CT were studied. Cancer risks, in the form of lifetime attributable risk (LAR) of cancer incidence, were estimated by linear extrapolation using the organ radiation doses and the LAR data.

Results

The effective doses for head, thorax, abdomen and pelvis CT, were 0.7 mSv, 3.5 mSv, 3.0 mSv, 1.3 mSv respectively. The organs with the highest dose were; for head CT, salivary gland (22.33 mGy); for thorax CT, breast (7.89 mGy); for abdomen CT, colon (6.62 mGy); for pelvis CT, bladder (4.28 mGy). The corresponding LARs for boys and girls were 0.015-0.053% and 0.034-0.155% respectively. The organs with highest LARs were; for head CT, thyroid gland (0.003% for boys, 0.015% for girls); for thorax CT, lung for boys (0.014%) and breast for girls (0.069%); for abdomen CT, colon for boys (0.017%) and lung for girls (0.016%); for pelvis CT, bladder for both boys and girls (0.008%).

Conclusion

The effective doses from these common pediatric CT examinations ranged from 0.7 mSv to 3.5 mSv and the associated lifetime cancer risks were found to be up to 0.16%, with some organs of higher radiosensitivity including breast, thyroid gland, colon and lungs.